Deepwater oil and gas exploration and production projects face many unique challenges that impact associated production facilities and drilling activities. Hurricanes and loop currents rank high on the list of challenges faced during deepwater operations. Hurricane and loop currents shorten the operability envelopes for drilling activity, and shutdown operations. These currents are particularly a problem when the vessel is connected to the ocean floor by a drilling riser. The currents pushing against a typical drilling riser of 52.25″ diameter can cause a force of as much as 100,000 lbs. When the riser is released from the ocean floor equipment under this kind of side loadings the resultant movement of the riser can cause the riser to hit parts of the vessel and cause major damage.
An important piece of information to have before releasing the riser from the seafloor for retrieval is the extent of the side force and the direction of the currents. Surface currents can literally be in one direction and the deeper currents can be in the opposite direction. Upon release it is possible for the riser to move in the opposite direction as one would expect based on surface current observations.
Current readings are primarily gathered today by having acoustic instruments focus on bits of trash floating at various depths and inferring the current speed and direction from that acoustinc reading. In a few days the rig operation will learn what the current profile is today. This usually involves the hiring of a vessel to sit near the rig in question to make these readings, at substantial expense.